[captain harlock]

Well, lets see, your first question should be given the answer yes. If the truck makes wheelies and then go from a current gear ratio to higher one, the higher one will decrease torque and as a result your truck will do less wheelies, but perhaps in most cases more speed. If your motor is a torqy motor then you can gear way higher than stock gearing, but when you are using a mild truck brushless system such as the HV-Maxx which produces arond 370-400 watts considered pretty low and weak to the wild ones like the Feigao 9l that gives around 1100-1200 watts, you must not exceed the usage of more than 1-2 teeth. I bet your E-Maxx is stock chassis, tires, etc..so you can use 1 or two additional teeth in your pinion gear or decrease 3-6 teeth from your spur gear. This will not heat up your controller to an extreme point, but it will be hot to the point where it will not thermal, however, if it thermals, then you should deduct some teeth from your pinion or induct more gears to your spur. Doing so you will gain the motor more effeciency which means less heat. If you are going to use 14 teeht pinion then there is not any real problem, just make sure that the controller does not thermal and if it does, just forget about the 14t and get back to the 12t.